FIG. 1 is a view for explaining a general network configuration that enables two-way data communications among specific information terminals (to be simply referred to as “PC” hereinafter). As shown in FIG. 1, a plurality of local networks 20A, 20B are connected to a data communication network such as the Internet 10 by representative nodes 21A, 21B. The data communication network means a computer network that is configured by a plurality of types of wired/wireless transmission media. The local networks 20A, 20B are closed networks capable of communicating data with nodes in a previously permitted range, in which in general each of the PCs can transmit/receive the data to/from the data communication network outside the local networks only through at least one predetermined node. For instance, out of networks each having a node group configured by a plurality of multi-hierarchical routers, a network in which one of the routers functions as a representative node is included in the local networks 20A, 20B.
The above-described network configuration in which the plurality of local networks 20A, 20B are connected to the Internet 10 is widely used as a configuration for constructing an intranet that can be connected to the Internet, or, for example, a TV conference system that communicates data with business facilities with a company.
Here, the local network 20A is configured by the representative node 21A serving as a highest relay node, and a plurality of PCs 221A to 224A disposed in lower layers of the representative node 21A. The local network 20B, too, is configured by the representative node 21B serving as a highest relay node and a plurality of PCs 221B to 224B disposed in lower layers of the representative node 21B. In both of the local networks 20A, 20B, the PCs 221A to 224A and 221B to 224B communicate data with the Internet 10 non-synchronously via the representative nodes 21A, 21B.
However, in recent years, data exchange in a TV conference and the like using an inexpensive Internet has become popular, as well as transmission/reception of a large volume of data among an unspecified number of PCs. When such a situation becomes normal, the network configuration shown in FIG. 1 where the direct access of the PCs 221A to 224A and 221B to 224B of the local networks 20A, 20B an external network is limited, most of the communication bands of the representative nodes 21A, 21B is often occupied by some of the PCs that communicate data. In such a case, the representative nodes 21A, 21B inevitably become bottlenecks, lowering the communication performances in the local networks 20A, 20B. Moreover, in the current situation, the communication qualities significantly fluctuate geographically and temporally due to fluctuations in the performances of network resources. For this reason, it is urgent that the network resources be utilized effectively and that the communication performances be improved.
For example, Patent Document 1 discloses a technology for improving the communication performance of the entire wireless communication system by enabling a simultaneous connection between a wireless base station and a number of terminals while maintaining a constant communication quality in a wireless line where a transmission rate change momentarily. Patent Document 2, on the other hand, discloses a technology for optimizing the communication quality of a communication system while maintaining the communication performance thereof by adjusting the image quality of transmittable/receivable data in accordance with a terminal performance/line quality.